*Purpose: Tacrolimus (tac), a calcineurin inhibitor, is associated with multiple adverse effects when used for immunosuppression following kidney transplant (KT). Belatacept (bela) is a monoclonal antibody that blocks the co-stimulatory T-cell activation pathway that has been shown to be effective with a favorable side effect profile. However, studies assessing long-term infectious complications with bela compared to tac are limited. The purpose of this study was to determine the incidence of infections in patients converted to bela compared to those maintained on tac.

*Methods: In this retrospective study, KT recipients receiving bela between 2012 and 2020 were matched 1:1 to those receiving tac based on transplant date, decade of age, induction immunosuppression, and CMV mismatch. Tac patients were followed from the matched date of bela conversion. Baseline demographics collected were cause of kidney failure, bela dosage, incidence of infections, hospitalizations, biopsy-proven acute rejection (BPAR) and mortality. Patients were followed until study conclusion, death, or discontinuation of bela. The primary outcome was the incidence of an infection. Outcome data was calculated using chi-square, Fisher’s exact test, or student’s t-test where appropriate.

*Results: A total of 328 matched patients (164 bela, 164 tacrolimus) were included in the analysis with no differences in baseline characteristics. Median time from transplantation to bela conversion was 254 days (IQR 102 – 597). Median time of overall bela exposure was 584 days (IQR 274 – 1022). 119 patients had at least one infection, 42.7% in bela vs 29.9% in tac (RR 0.7; 95% CI: 0.520 – 0.936). Median time to infection post-conversion was 304 days in bela vs 267 days in tac (p = 0.927). There were no significant differences in the incidence of infections between groups, except for bacterial pneumonia leading to hospitalization which occurred in 11 patients; 10 in bela and 1 in tac (RR 0.1; 95% CI: 0.017 – 0.595). There were 43 initial episodes of BPAR post-conversion, 65.1% in bela vs 34.9% in tac (RR 0.5; 95% CI: 0.299 – 0.954).

*Conclusions: In this retrospective analysis of KT recipients, bela was associated with a higher rate of bacterial pneumonia leading to hospitalization and BPAR compared to tac.

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